Process for producing 2,3,3,3-tetrafluoropropene

ABSTRACT

This invention provides a process for producing 2,3,3,3-tetrafluoropropene, the process comprising: (1) a first reaction step of reacting hydrogen fluoride with at least one chlorine-containing compound selected from the group consisting of a chloropropane represented by Formula (1): CClX 2 CHClCH 2 Cl, wherein each X is the same or different and is CI or F, a chloropropene represented by Formula (2): CClY 2 CCl═CH 2 , wherein each Y is the same or different and is CI or F, and a chloropropene represented by Formula (3): CZ 2 ═CClCH 2 Cl, wherein each Z is the same or different and is CI or F in a gas phase in the absence of a catalyst while heating; and (2) a second reaction step of reacting hydrogen fluoride with a reaction product obtained in the first reaction step in a gas phase in the presence of a fluorination catalyst while heating. According to the process of this invention, 2,3,3,3-tetrafluoropropene (HFO-1234yf) can be obtained with high selectivity, and catalyst deterioration can be suppressed.

This application claims the benefit of U.S. provisional application Ser.No. 61/407,158 filed Oct. 27, 2010.

TECHNICAL FIELD

The present invention relates to a process for producing2,3,3,3-tetrafluoropropene.

BACKGROUND ART

Alternative refrigerants such as HFC-125 (C₂HF₅) and HFC-32 (CH₂F₂) havebeen widely used as important replacements for CFC, HCFC, etc., whichcause ozone layer depletion. However, these alternative refrigerants arepotent global warming substances, thus creating concern that diffusionof the refrigerants would increase global warming. As a preventivemeasure, these refrigerants are recovered after use. However, completerecovery of the refrigerants is impossible. In addition, the diffusionof these refrigerants due to leakage, etc., cannot be ignored. The useof CO₂ or hydrocarbon-based substances as alternative refrigerants hasalso been investigated. However, because CO₂ refrigerants have lowefficiency and devices using such refrigerants inevitably become large,CO₂ refrigerants have many problems in terms of the overall reduction ofgreenhouse gas emissions, including energy to be consumed. Furthermore,hydrocarbon-based substances pose safety problems due to their highflammability.

2,3,3,3-tetrafluoropropene (HFO-1234yf, CF₃CF═CH₂), which is an olefinicHFC having a low global warming potential, has recently been attractingattention as a material to solve the above problems. HFO-1234yf, usedalone or in combination with other substances, such ashydrofluorocarbons, hydrofluoroolefins, and hydrochlorofluoroolefins, isexpected to be useful as a refrigerant, and additionally as a blowingagent, propellant, extinguishing agent, or the like.

Some processes for producing HFO-1234yf have been disclosed. In most ofthese processes, a hydrohalopropane such as a hydrochloropropane or ahydrohalopropene such as a hydrochloropropene, used as a startingmaterial, is fluorinated with hydrogen fluoride to ultimately prepareHFO-1234yf.

For example, Patent Literature 1 listed below discloses a process inwhich HFO-1234yf is produced, via a hydrochlorofluoroalkane or ahydrochlorofluoroalkene, by subjecting a haloalkane or a haloalkene as astarting material to fluorination with HF, dehydrochlorination, etc.

Patent Literature 2 listed below discloses a process in which HFO-1234yfis produced, via a hydrochlorofluoroalkane, hydrochlorofluoroalkene,etc., by subjecting a hydrochloropropane, hydrochlorofluoropropane,etc., as a starting material to fluorination with HF in the presence ofa catalyst.

Furthermore, Patent Literature 3 listed below discloses an integrationprocess for preparing HFO-1234yf by using 1,1,1,2,3-pentachloropropane(HCC-240 db) as a starting material, fluorinating the starting materialwith HF to produce HCFO-1233xf, and then adding HF to the thus-obtainedHCFO-1233xf to produce HCFC-244bb, followed by dehydrochlorination.

All of these processes use a hydrochlorocarbon as a starting material toprepare HFO-1234yf by a multiple-stage reaction process. However, eachof the processes has a problem of a cost increase due to the use of acatalyst and also has a drawback of insufficient selectivity resultingfrom the formation of many products other than the desired product,i.e., HFO-1234yf. Further, the use of higher chlorinate as a startingmaterial poses another problem in that catalyst activity is likely todeteriorate as reaction progresses.

CITATION LIST Patent Literature

-   PTL 1: WO2007/079431-   PTL 2: WO2008/054781-   PTL 3: Japanese Unexamined Patent Publication No. 2009-227675

SUMMARY OF INVENTION Technical Problem

The present invention has been accomplished in view of the foregoingstate of the art and its primary object is to provide a productionprocess that is capable of producing 2,3,3,3-tetrafluoropropene(HFO-1234yf) in good yield, using a chloropropane compound orchloropropene compound as a starting material, and that is suitable foruse on an industrial scale.

Solution to Problem

The present inventors conducted extensive investigations to achieve theabove object and found that selectivity of the desired2,3,3,3-tetrafluoropropene (HFO-1234yf) can be improved, catalystdeterioration can be suppressed, and HFO-1234yf can be producedefficiently on an industrial scale according to a two-stage reactionprocess in which a chloropropane compound or chloropropene compoundrepresented by a specific general formula, which is used as a startingmaterial, is reacted with hydrogen fluoride in a gas phase in theabsence of a catalyst while heating, and subsequently the productobtained by said reaction is reacted with hydrogen fluoride in a gasphase in the presence of a fluorination catalyst while heating. Thepresent invention has been accomplished based on this finding.

More specifically, the present invention provides the following processfor producing 2,3,3,3-tetrafluoropropene.

Item 1. A process for producing 2,3,3,3-tetrafluoropropene, the processcomprising:

(1) a first reaction step of reacting hydrogen fluoride with at leastone chlorine-containing compound selected from the group consisting of achloropropane represented by Formula (1): CClX₂CHClCH₂Cl, wherein each Xis the same or different and is Cl or F, a chloropropene represented byFormula (2): CClY₂CCl═CH₂, wherein each Y is the same or different andis Cl or F, and a chloropropene represented by Formula (3):CZ₂═CClCH₂Cl, wherein each Z is the same or different and is Cl or F ina gas phase in the absence of a catalyst while heating; and

(2) a second reaction step of reacting a reaction product obtained inthe first reaction step with hydrogen fluoride in a gas phase in thepresence of a fluorination catalyst while heating.

Item 2. The process according to Item 1, wherein the reactiontemperature in the first reaction step is 250 to 600° C., and thereaction temperature in the second reaction step is 200 to 500° C.

Item 3. The process according to Item 1 or 2, wherein the amount ofhydrogen fluoride in the first reaction step is 1 to 100 moles per moleof the chlorine-containing compound used as a starting material, and theamount of hydrogen fluoride in the second reaction step is 1 to 50 molesper mole of the chlorine-containing compound used as a starting materialin the first reaction step.

Item 4. The process according to any one of Items 1 to 3, wherein thefluorination catalyst used in the second reaction step is at least onemember selected from the group consisting of chromium oxides, chromiumoxyfluorides, aluminium fluorides, aluminum oxyfluorides, and metalfluorides.

Item 5. The process according to any one of Items 1 to 4, wherein afterremoving hydrogen chloride from the reaction product obtained in thefirst reaction step, the reaction product is used as a starting materialin the second reaction step.

Item 6. The process according to any one of Items 1 to 5, wherein afterreducing the amount of hydrogen fluoride contained in the reactionproduct obtained in the first reaction step, the reaction product isused as a starting material in the second reaction step.

Item 7. The process according to any one of Items 1 to 6, wherein thesecond reaction step uses, as a starting material, at least onechlorine-containing compound selected from the group consisting of achloropropane represented by Formula (4): CClX₂CHClCH₂Cl, wherein atleast one of X is F, a chloropropene represented by Formula (5):CClY₂CCl═CH₂, wherein at least one of Y is F, and a chloropropenerepresented by Formula (6): CZ₂═CClCH₂Cl, wherein at least one of Z isF,

the chlorine-containing compound being contained in the reaction productobtained in the first reaction step.

Item 8. The process according to any one of Items 1 to 6, wherein thesecond reaction step uses, as a starting material, at least onechlorine-containing compound selected from the group consisting ofCF₂ClCHClCH₂Cl (HCFC-242dc) and CF₂ClCCl═CH₂(HCFO-1232xf),

the chlorine-containing compound being contained in the reaction productobtained in the first reaction step.

Item 9. The process according to any one of Items 1 to 8, wherein thefirst reaction step is conducted in a reactor made of an alloycontaining 30% or more by weight of nickel.

Item 10. The process according to Item 9, wherein the alloy containing30% or more by weight of nickel is at least one member selected from thegroup consisting of Hastelloy, Inconel, Monel, and Incoloy.

The process for producing 2,3,3,3-tetrafluoropropene of the presentinvention is described in detail below.

(1) Starting Compound

In the present invention, at least one chlorine-containing compoundselected from the group consisting of a chloropropane represented byFormula (1): CClX₂CHClCH₂Cl, wherein each X is the same or different andis Cl or F, a chloropropene represented by Formula (2): CClY₂CCl═CH₂,wherein each Y is the same or different and is Cl or F, and achloropropene represented by Formula (3): CZ₂═CClCH₂Cl, wherein each Zis the same or different and is Cl or F is used as a starting compound.When these chlorine-containing compounds are used as a starting materialand reacted with hydrogen fluoride in a two-stage reaction processaccording to the conditions described below, the desired2,3,3,3-tetrafluoropropene (HFO-1234yf) can be obtained with highselectivity as compared to the case in which fluorination reaction isconducted in a single-stage reaction process.

Among the starting compounds, specific examples of the chloropropanerepresented by Formula (1): CClX₂CHClCH₂Cl include CCl₃CHClCH₂Cl(HCC-240 db, bp. 179° C./760 mmHg, 51-53° C./3 mmHg), CFCl₂CHClCH₂Cl(HCFC-241 db, bp. 157° C.), CF₂ClCHClCH₂Cl (HCFC-242dc, bp. 113-114°C.), and the like. Specific examples of the chloropropene represented byFormula (2): CClY₂CCl═CH₂ include CCl₃CCl═CH₂(HCO-1230xf, bp. 128° C.),CFCl₂CCl═CH₂(HCFO-1231xf, bp. 98.5-99° C.), CF₂ClCCl═CH₂(HCFO-1232xf,bp. 57-58° C.), and the like. Specific examples of the chloropropenerepresented by Formula (3): CZ₂═CClCH₂Cl include CCl₂═CClCH₂Cl(HCO-1230xa, bp. 138° C.), CFCl═CClCH₂Cl (HCFO-1231xb), CF₂═CClCH₂Cl(HCFO-1232xc), and the like.

Among these starting compounds, HCC-240 db (CCl₃CHClCH₂Cl(1,1,1,2,3-pentachloropropane)), HCO-1230xf (CCl₃CCl═CH₂(2,3,3,3-tetrachloropropene)), and HCO-1230xa (CCl₂═CClCH₂Cl(1,1,2,3-tetrachloropropene)) are particularly advantageous startingcompounds in that they are readily available and inexpensive.

In the present invention, the starting compounds can be used singly orin combination of two or more.

(2) Production Process

In the present invention, it is necessary to adopt a two-stage reactionprocess comprising a first reaction step of reacting at least one of theaforementioned starting compounds with hydrogen fluoride in a gas phasein the absence of a catalyst while heating, and a second reaction stepof reacting the reaction product obtained in the first reaction stepwith hydrogen fluoride in a gas phase in the presence of a fluorinationcatalyst while heating. The use of such a two-stage reaction processenables the improvement of selectivity of the desired2,3,3,3-tetrafluoropropene (HFO-1234yf) and further enables thesuppression of deterioration of a catalyst used in the fluorinationprocess.

Each reaction step will be described below in detail.

(i) First Reaction Step

In the first reaction step, at least one of the above starting compoundsis reacted with hydrogen fluoride in a gas phase in the absence of acatalyst while heating.

In the first reaction step, the reaction of the starting compound withhydrogen fluoride under such conditions yields a product containing2-chloro-3,3,3-trifluoropropene (HCFO-1233xf) that is an intermediatefor 2,3,3,3-tetrafluoropropene (HFO-1234yf).

The first reaction step requires the reaction of the starting compoundwith hydrogen fluoride in a gas phase in the absence of a catalyst. Aslong as the starting compound and hydrogen fluoride come into contactwith each other in a gas phase within the reaction temperature rangedescried below, the starting compound may be in a liquid form whensupplied. For example, when the starting compound is liquid at anordinary temperature and ordinary pressure, the starting compound isvaporized using a vaporizer (vaporization region), passed through apreheating region, and then supplied to a mixing region wherein thestarting compound is contacted with anhydrous hydrogen fluoride, wherebythe reaction can be conducted in a gas phase. The reaction may also becarried out by supplying the starting compound in a liquid phase to areactor, and vaporizing the compound when the compound enters a reactiontemperature range to react with hydrogen fluoride. There is noparticular limitation to the methods for vaporizing the startingcompound in the reaction temperature range. The starting compound may bevaporized into a gas phase by, for example, filling a reaction tube witha material that exhibits excellent thermal conductivity, exerts nocatalytic activity in the reaction of the present invention, and isstable to hydrogen fluoride, such as metal pieces of corrosion-resistantmaterials including nickel beads, alumina beads, Hastelloy, Inconel,Monel, Incoloy, and the like, so as to homogenize the temperaturedistribution within the reaction tube; heating the reaction tube to notless than the vaporization temperature of the starting compound; andsupplying the starting compound in a liquid phase thereinto.

Hydrogen fluoride may generally be supplied to a reactor in a gas phasetogether with the starting compound. The amount of the hydrogen fluoridesupplied is generally about 1 to about 100 moles, preferably about 5 toabout 50 moles, and more preferably about 15 to about 25 moles, per molof the aforementioned starting compound. By setting the amount withinsuch a range, the conversion of the starting compound and theselectivity of components, such as 2-chloro-3,3,3-trifluoropropene(HCFO-1233xf), that can be intermediates for 2,3,3,3-tetrafluoropropene(HFO-1234yf), can be maintained in a desirable range.

The starting compound may be supplied to the reactor as is or may bediluted with an inert gas such as nitrogen, helium, or argon and thensupplied to the reactor.

The form of the reactor used in the first reaction step is notparticularly limited. Examples of usable reactors include a fistulousadiabatic reactor, or an adiabatic reactor packed with a porous ornonporous metal or medium that improves the gas-phase mixing statebetween hydrogen fluoride and the starting material. Also usable is amultitubular reactor or the like in which a heating medium is used tocool the reactor and to homogenize the temperature distribution withinthe reactor. When fistulous reactors are used in the method using areaction tube having a small inner diameter to improve the heat transferefficiency, the relationship of the flow rate of the starting compoundto the inner diameter of the reaction tube, for example, is preferablyadjusted so as to achieve a high linear velocity and a large heatingarea.

The reactor is preferably made of an alloy containing 30% or more byweight of nickel. More specifically, a reactor formed of a material thatis resistant to the corrosive action of hydrogen fluoride, such asHastelloy, Inconel, Monel, and Incoloy, is preferably used.

In the first reaction step, the reaction temperature, i.e., thetemperature in the reactor, is about 250° C. to about 600° C.,preferably about 300° C. to about 500° C., and more preferably about350° C. to about 450° C. If the reaction temperature is higher than thisrange, the selectivity of components, such as HCFO-1233xf, that can beintermediates for 2,3,3,3-tetrafluoropropene (HFO-1234yf) undesirablydecreases. If the reaction temperature is lower than this range, theconversion of the starting compound undesirably decreases.

The pressure during the reaction is not particularly limited, as long asthe starting compound and hydrogen fluoride can be present in the formof a gas phase, and the reaction may be conducted under ordinarypressure, increased pressure, or reduced pressure. More specifically,the first reaction step may be conducted under reduced pressure oratmospheric pressure (0.1 MPa). This step also may be conducted underincreased pressure at which the starting material does not turn into aliquid phase.

The reaction time is not particularly limited. However, the residencetime, which is represented by V/Fo, may be generally adjusted to a rangeof about 1 to about 10 sec. V/Fo is the ratio of the reaction space V(cc) in a gas phase to the total flow rate Fo (flow rate at 0° C., 0.1MPa: cc/sec) of the starting material gases (starting compound, hydrogenfluoride and inert gas) supplied to the reaction system.

Under the above reaction conditions, a reaction product that contains2-chloro-3,3,3-trifluoropropene (HCFO-1233xf) can be obtained at thereactor outlet.

(ii) Second Reaction Step

In the second reaction step, the product obtained in the first reactionstep is used as a starting material to be reacted with hydrogen fluoridein a gas phase in the presence of a fluorination catalyst while heating.

The product obtained in the first reaction step contains2-chloro-3,3,3-trifluoropropene (HCFO-1233xf) as a main component andalso contains at least one chlorine-containing compound selected fromthe group consisting of a chloropropane represented by Formula (4):CClX₂CHClCH₂Cl, wherein at least one of X is F, a chloropropenerepresented by Formula (5): CClY₂CCl═CH₂, wherein at least one of Y isF, and a chloropropene represented by Formula (6): CZ₂═CClCH₂Cl, whereinat least one of Z is F. More specifically, the reaction product alsocontains a chloropropane compound or a chloropropene compound, such as1,2,3-trichloro-1,1-difluoropropane (HCFC-242dc) and2,3-dichloro-3,3-difluoropropene (HCFO-1232xf). When the productcontaining the chloropropane compound, chloropropene compound, or thelike is used as is as a starting material and reacted with hydrogenfluoride in the presence of a fluorination catalyst in the secondreaction step, not only HCFO-1233xf but also the components contained inthe product, such as HCFC-242dc and HCFO-1232xf, can be converted to2,3,3,3-tetrafluoropropene (HFO-1234yf). As a result, the desiredHFO-1234yf can be obtained with high selectivity. Above all, in thepresent invention, at least one of HCFC-242dc and HCFO-1232xf ispreferably used together with HCFO-1233xf as the starting material inthe second reaction step.

Moreover, since a fluorination catalyst is used only in the secondreaction step, catalyst deterioration is significantly suppressedrelative to the amount of produced HFO-1234yf, as compared to the casein which HFO-1234yf is produced by a single-stage fluorination reaction.This ensures an economically excellent production process.

In contrast, it is not favorable that only HCFO-1233xf is separated fromthe product obtained in the first reaction step and used in a reactionfor synthesizing HFO-1234yf, while other components, such as achloropropane compound and chloropropene compound, are recycled as thestarting material in the first reaction step, because the selectivity ofHCFO-1233xf in the first reaction step is unexpectedly decreased,resulting in the decrease in overall selectivity of HFO-1234yf.

As a fluorination catalyst used in the second reaction step, a knowncatalyst having activity to fluorination reaction with hydrogen fluoridemay be used. For example, metal oxides or metal oxyfluorides, such aschromium oxides, chromium oxyfluorides, aluminium fluorides, andaluminum oxyfluorides, may be used. In addition to these catalysts,metal fluorides, such as MgF₂, TaF₅, and SbF₅, also may be used.

Among these catalysts, the chromium oxides, for instance, are notparticularly limited. For example, it is preferable to use chromiumoxide represented by the composition formula: CrOm, wherein preferably1.5<m<3, more preferably 2<m<2.75, and even more preferably 2<m<2.3. Anychromium oxide catalysts in the form of powder, pellets, etc., can beused, as long as they are suitable for the reaction. In particular,pellet-form catalysts are preferred. The above chromium oxide catalystscan be produced, for example, by the process disclosed in JapaneseUnexamined Patent Publication No. H5-146680.

In addition, the fluorinated chromium oxides can be prepared by theprocess disclosed in Japanese Unexamined Patent Publication No.H5-146680. For example, they can be prepared by fluorinating thechromium oxide obtained by the above-described process with hydrogenfluoride (HF treatment).

The degree of fluorination is not particularly limited. For example, afluorinated chromium oxide having a fluorine content of about 10 toabout 45% by weight may be suitably used.

Further, the chromium-based catalyst disclosed in Japanese UnexaminedPatent Publication No. H11-171806 also may be used as a chromium oxidecatalyst or fluorinated chrome oxide catalyst. The chromium-basedcatalyst is in an amorphous state and comprises, as a main component, achromium compound containing at least one metallic element selected fromthe group consisting of indium, gallium, cobalt, nickel, zinc, andaluminum. The chromium in the chromium compound has an average valencenumber of not less than +3.5 and not more than +5.0.

The above-described fluorination catalyst may be used as supported on acarrier such as alumina and activated carbon.

Anhydrous hydrogen fluoride used as a starting material may be generallysupplied to a reactor in the form of a gas phase together with thereaction product obtained in the first reaction step. The amount ofhydrogen fluoride supplied in the second reaction step may be determinedbased on the amount of said at least one chlorine-containing compoundselected from the group consisting of a chloropropane represented byFormula (1): CClX₂CHClCH₂Cl, a chloropropene represented by Formula (2):CClY₂CCl═CH₂, and a chloropropene represented by Formula (3):CZ₂═CClCH₂Cl, used as a starting material in the first reaction step.Specifically, the amount of hydrogen fluoride is about 1 to about 50moles, preferably about 5 to about 30 moles, and more preferably about 7to about 15 moles, per mole of said at least one chlorine-containingcompound. The amount of hydrogen fluoride supplied in the secondreaction step is preferably within the above-described range and smallerthan the amount of hydrogen fluoride actually supplied in the firstreaction step.

When the amount of hydrogen fluoride contained in the reaction productobtained in the first reaction step is within the aforementioned range,a fluorination reaction in the second reaction step can be conducted byusing only the reaction product without adding further hydrogenfluoride. When the amount of hydrogen fluoride contained in the reactionproduct obtained in the first reaction step is larger than theaforementioned range, the reaction product may be used as a startingmaterial in the second reaction step after reducing the amount ofhydrogen fluoride contained therein by a method such as distillation.

The selectivity of 2,3,3,3-tetrafluoropropene (HFO-1234yf) can bemaintained in a desirable range by using anhydrous hydrogen fluoridewithin the above-described range in the presence of a fluorinationcatalyst.

To maintain catalyst activity for a long period of time, oxygen may besupplied to the reactor as entrained with the aforementioned startingmaterial, especially in the second reaction step. In this case, theamount of oxygen to be supplied may be about 0.01 to about 0.3 mole permole of the chlorine-containing compound supplied as a starting materialin the first reaction step.

The form of the reactor used in the second reaction step is notparticularly limited. Examples of usable reactors include an adiabaticreactor packed with a catalyst and a multitubular reactor in which aheating medium is used to cool the reactor. As in the first reactionstep, a reactor formed of a material that is resistant to the corrosiveaction of hydrogen fluoride, such as Hastelloy, Inconel, and Monel, ispreferably used.

In the second reaction step, the reaction temperature, i.e., thetemperature in the reactor, is about 200° C. to about 500° C.,preferably about 300° C. to about 450° C., and more preferably about350° C. to about 400° C. If the reaction temperature is higher than thisrange, the selectivity of HFO-1234yf undesirably decreases. If thereaction temperature is lower than this range, the conversion of thestarting compound undesirably decreases. In particular, the reactiontemperature in the second reaction step is preferably within theabove-described range and lower than that in the first reaction step.

The pressure during the reaction is not particularly limited, and thereaction may be conducted under ordinary pressure or increased pressure.More specifically, the reaction in the present invention may beconducted under atmospheric pressure (0.1 MPa), and may be alsoconducted under an increased pressure up to about 1.0 MPa.

The reaction time is not particularly limited. However, the contacttime, which is represented by W/Fo, may be generally adjusted to a rangeof about 5 to about 20 g·sec/cc. W/Fo is the ratio of the amount ofpacked catalyst W (g) to the total flow rate of the starting materialgases supplied to the reactor in the second reaction step (total amountof product obtained in the first reaction step and HF) Fo (flow rate at0° C., 1 atm: cc/sec).

In the second reaction step, the product obtained in the first reactionstep may be supplied as is but is preferably supplied in the secondreaction step after removing hydrogen chloride contained therein. Due tothis, the effects of reducing energy loss caused by handling hydrogenchloride that is unnecessary in the second reaction step and improvingthe selectivity of HFO-1234yf can be expected. Methods for removinghydrogen chloride from the product obtained in the first reaction stepare not particularly limited. For example, hydrogen chloride can beeasily removed as a column top product by distillation.

As described above, when the product obtained in the first reaction stepcontains more than the amount of hydrogen fluoride required in thesecond reaction step, it may be supplied to the reactor in the secondreaction step after removing excessive hydrogen fluoride from theproduct obtained in the first reaction step to reduce the content ofhydrogen fluoride. Methods for removing hydrogen fluoride are also notparticularly limited. For example, according to a method for separatinghydrogen fluoride by distillation or a method for extracting a phasesubstantially consisting of hydrogen fluoride by liquid-liquidseparation, the amount of hydrogen fluoride contained in the product canbe reduced by a simple method.

(3) Reaction Product:

According to the aforementioned process comprising two-stage reactionsteps, a reaction product that contains the desired2,3,3,3-tetrafluoropropene (HFO-1234yf) can be obtained with highselectivity at the reactor outlet in the second reaction step. Theobtained HFO-1234yf can be purified and collected by distillation, etc.

In the production process of the present invention, the reaction productcontains not only HFO-1234yf but also other components, such as hydrogenchloride, unreacted hydrogen fluoride, and CF₃CCl═CH₂(HCFO-1233xf). Inaddition to these components, the reaction product may contain achlorofluoropropane compound, chlorofluoropropene compound, etc., suchas CFCl₂CHClCH₂Cl (HCFC-241 db), CFCl₂CCl═CH₂(HCFO-1231xf),CF₂ClCHClCH₂Cl (HCFC-242dc), CF₂ClCCl═CH₂(HCFO-1232xf), and CF₃CHClCH₂Cl(HCFC-243 db). These compounds are produced as a precursor forHFO-1234yf according to the type of starting material used or reactionconditions, and can be reused as a starting material in the firstreaction step or second reaction step. In particular, when HCFO-1233xf,HCFO-1232xf, or HCFC-242dc is reused as a starting material in thesecond reaction step, the desired HFO-1234yf can be obtained with highselectivity.

FIG. 1 is a flowchart that shows one embodiment of the process of thepresent invention, which is a process comprising a step of producingHFO-1234yf according to the process of the present invention and asubsequent purification step.

In the process shown in FIG. 1, 1,1,1,2,3-pentachloropropane (HCC-240db) is used as a starting material and supplied to a reactor (1)together with hydrogen fluoride to conduct the reaction of the firstreaction step in the absence of a catalyst. The product obtained fromthe reactor (1) is sent to a distillation column (1)-1 to removehydrogen chloride as a column top product. After that, other componentsare sent to a distillation column (1)-2 to remove excessive hydrogenfluoride as a column bottom product, and then the remainder is suppliedto a reactor (2). The hydrogen fluoride separated in the distillationcolumn (1)-2 can be recycled by sending it to the reactor (1) and reusedas a starting material.

In the reactor (2), the reaction of the product obtained from the firstreaction step with hydrogen fluoride in the presence of a fluorinationcatalyst is conducted as the second reaction step. After removinghydrogen chloride as a column top product in a distillation column(2)-1, the product obtained from the reactor (2) is sent to adistillation column (2)-2 to remove unreacted products and by-products,such as hydrogen fluoride, HCFO-1233xf, HCFC-242dc, and HCFO-1232xf, andother components are sent to a distillation column (2)-3. The removedhydrogen fluoride, HCFO-1233xf, HCFC-242dc, HCFO-1232xf, etc., can bereused as a starting material for the reactor (2).

In the distillation column (2)-3, the desired 2,3,3,3-tetrafluoropropene(HFO-1234yf) can be obtained by removing hydrogen fluoride as a columnbottom product. The hydrogen fluoride obtained in the distillationcolumn (2)-3 can be sent to the reactor (1) and reused as a startingmaterial.

The desired HFO-1234yf obtained in the distillation column (2)-3 can befurther subjected to a crude purification step and a fine purificationstep to yield a final product. Specific methods for the crudepurification step and the fine purification step are not particularlylimited. For example, water washing, dehydration (drying), distillation,liquid separation or other means can be applied to the steps.

Advantageous Effects of Invention

According to the process for producing 2,3,3,3-tetrafluoropropene of thepresent invention, 2,3,3,3-tetrafluoropropene (HFO-1234yf) can beobtained with high selectivity, and catalyst deterioration can besuppressed. Accordingly, the process of the present invention is highlyuseful as a process for producing 2,3,3,3-tetrafluoropropene that issuitable for use on an industrial scale.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flowchart showing one embodiment of the process of thepresent invention.

DESCRIPTION OF EMBODIMENTS

An Example is given below to illustrate the present invention in moredetail.

EXAMPLE 1 (1) First Reaction Step

A ½-inch pipe made of Inconel (inner diameter: 1.02 cm) equipped with a⅛-inch thermometer protection tube made of Inconel (outer diameter: 0.32cm) was used as a reaction tube and was packed with nickel beads(diameter: 3 mm) that were inactive to the reaction. The packed nickelbead bed length was 19.5 cm, and the space volume of the packed bed ofnickel beads was 7.5 cm³.

To this reaction tube, 1,1,1,2,3-pentachloropropane (HCC-240 db) andanhydrous hydrogen fluoride were continuously supplied at a rate of 2.4cc/min (flow rate at 0° C. and 0.1 MPa) and at a rate of 47 cc/min (flowrate at 0° C. and 0.1 MPa), respectively. The temperature inside thereaction tube was set at 400° C. and the pressure inside the reactiontube was set at atmospheric pressure (0.1 MPa).

The molar ratio of HF to HCC-240 db was 20, and the residence time(V/Fo), which is the ratio of the space volume (V) of the packed bed ofnickel beads to the total flow rate (Fo) of HCC-240 db and HF, was 8.0sec.

Effluents obtained from the reactor 65 hours after the start of reactionwere analyzed by gas chromatography. The conversion of HCC-240 db was100%. Table 1 below shows the selectivity of each component.

TABLE 1 Component Selectivity (%) HCFO-1233xf 88 HCFC-242dc 8.1HCFO-1232xf 2.8 Others 1.1

(2) Treatment for Removing Hydrogen Chloride and Hydrogen Fluoride

Hydrogen chloride was removed from the product obtained in the firstreaction step by distillation, and further, distillation was conductedto reduce the amount of hydrogen fluoride. A commonly used distillationcolumn was used for distillation for removing the HCl. The column had atheoretical plate number of 20, a column top pressure of 0.7 MPa, acolumn top temperature of −42° C., and a column bottom temperature of62° C. A distillation column used for reducing the amount of HF had atheoretical plate number of 30, an operating pressure of 0.2 MPa, acolumn top temperature of 47° C., and a column bottom temperature of 74°C. From the top of this distillation column, organic matter mainlyincluding HF and HFO-1233xf was extracted. From the bottom of thecolumn, organic matter mainly including HCFC-242dc was extracted. Fromthe middle portion of the column, HF was extracted. The composition ofcolumn top products and column bottom products after distillation wasanalyzed by gas chromatography and by titration with NaOH aqueoussolution. The results are shown in Table 2 below.

TABLE 2 Distillation column material balance (mol/hr) Top of Middle theportion of Bottom of Component Feed column the column the column HF1.676 0.959 0.699 0.018 HCFO-1233xf 0.084 0.084 trace trace HCFC-242dc0.0077 trace trace 0.0077 HCFO-1232xf 0.0027 trace trace 0.0027 Others0.001 trace trace 0.001

(3) Second Reaction Step

A tubular reactor made of Hastelloy having an inner diameter of 15 mmand a length of 1 m was packed with 22 g of a fluorinated chromium oxidecatalyst (fluorine content: about 15.0%) that had been obtained bysubjecting chromium oxide to fluorination treatment. The fluorinatedchromium oxide catalyst was prepared by the following procedure. First,114 g of 10% ammonia water was added to 765 g of a 5.7% aqueous solutionof chromium nitrate. After the resulting precipitate was filtered andwashed, it was dried in air for 12 hours at 120° C. to give a chromiumhydroxide. The chromium hydroxide was formed into pellets having adiameter of 3.0 mm and a height of 3.0 mm and calcined in a nitrogenstream for two hours at 400° C. A reactor made of Hastelloy C was filledwith the obtained chromium oxide in the form of pellets. Increasing thetemperature gradually from 200 to 360° C., the chromium oxide was heatedand fluorinated with dilute HF in which hydrogen fluoride had beendiluted to 20 vol % with nitrogen. After the temperature reached 360°C., the chromium oxide was further fluorinated with 100% HF to preparethe fluorinated chromium oxide catalyst.

The temperature inside the reaction tube was set at 365° C., and thepressure inside the reaction tube was set at atmospheric pressure (0.1MPa). Anhydrous hydrogen fluoride (HF) gas was supplied to the reactorat a flow rate of 118 cc/min (flow rate at 0° C., 0.1 MPa; the sameapplies hereinafter), oxygen gas was fed to the reactor at a flow rateof 2.2 cc/min, and these reaction conditions were maintained for onehour. After that, the mixture of the compounds obtained as column topand column bottom products in the treatment for removing hydrogenfluoride described above (molar ratio ofHCFO-1233xf:HCFC-242dc:HCFO-1232xf is 89:8.1:2.9) was supplied to thereactor at a flow rate of 12.7 cc/min.

At that point, the molar ratio of the HF to the starting materialsupplied to the reactor in the second reaction step was 9.3:1. The ratio(W/Fo) of the amount of packed catalyst W (g) to the total flow rate ofthe starting material gases supplied to the reactor in the secondreaction step (total amount of column top products in step (2) and HF)Fo (flow rate at 0° C., 0.1 MPa: cc/sec) was 9.9.

Effluents obtained from the reactor 28 hours after the start of reactionwere analyzed by gas chromatography. The conversion of HCFO-1233xfsupplied to the reactor in the second reaction step was 24%, and theconversion of HCFC-242dc and HCFO-1232xf supplied to the reactor in thesecond reaction step was 100%. Table 3 below shows the composition ofthe organic matter obtained at the reactor outlet.

TABLE 3 Composition at the Component reactor outlet (%) HFO-1234yf 15HFC-245cb 3.3 HCFC-242dc 0 HCFO-1232xf 0 HCFO-1233xf 76 Others 5.7

From the above results, it was confirmed that according to theproduction process of the present invention, HFO-1234yf can be obtainedwith high selectivity. Other components can be recycled as a startingmaterial in the first or second reaction step.

The invention claimed is:
 1. A process for producing2,3,3,3-tetrafluoropropene, the process comprising: (1) a first reactionstep of reacting hydrogen fluoride with at least one chlorine-containingcompound selected from the group consisting of a chloropropanerepresented by Formula (1): CClX₂CHClCH₂Cl, wherein each X is the sameor different and is Cl or F, a chloropropene represented by Formula (2):CClY₂CCl═CH₂, wherein each Y is the same or different and is Cl or F,and a chloropropene represented by Formula (3): CZ₂═CClCH₂Cl, whereineach Z is the same or different and is Cl or F in a gas phase in theabsence of a catalyst while heating; and (2) a second reaction step ofreacting a reaction product obtained in the first reaction step withhydrogen fluoride in a gas phase in the presence of a fluorinationcatalyst while heating, wherein the second reaction step uses, as astarting material, CF₃CCl═CH₂ (HCFO-1233xf) and at least onechlorine-containing compound selected from the group consisting ofCF₂ClCHClCH₂Cl (HCFC-242dc) and CF₂ClCCl═CH₂ (HCFO-1232xf), and whereinthe CF₃CCl═CH₂ (HCFO-1233xf) and the at least one chlorine-containingcompound are contained in the reaction product obtained in the firstreaction step.
 2. The process according to claim 1, wherein the reactiontemperature in the first reaction step is 250 to 600° C., and thereaction temperature in the second reaction step is 200 to 500° C. 3.The process according to claim 1, wherein the amount of hydrogenfluoride in the first reaction step is 1 to 100 moles per mole of thechlorine-containing compound used as a starting material, and the amountof hydrogen fluoride in the second reaction step is 1 to 50 moles permole of the chlorine-containing compound used as a starting material inthe first reaction step.
 4. The process according to claim 1, whereinthe fluorination catalyst used in the second reaction step is at leastone member selected from the group consisting of chromium oxides,chromium oxyfluorides, aluminium fluorides, aluminum oxyfluorides, andmetal fluorides.
 5. The process according to claim 1, wherein afterremoving hydrogen chloride from the reaction product obtained in thefirst reaction step, the CF₃CCl═CH₂ (HCFO-1233xf) and the at least onechlorine-containing compound contained in the reaction product obtainedin the first reaction step are used as a starting material in the secondreaction step.
 6. The process according to claim 1, wherein afterreducing the amount of hydrogen fluoride contained in the reactionproduct obtained in the first reaction step, the CF₃CCl═CH₂(HCFO-1233xf) and the at least one chlorine-containing compoundcontained in the reaction product obtained in the first reaction stepare used as a starting material in the second reaction step.
 7. Theprocess according to claim 1, wherein the first reaction step isconducted in a reactor made of an alloy containing 30% or more by weightof nickel.
 8. The process according to claim 7, wherein the alloycontaining 30% or more by weight of nickel is at least one memberselected from the group consisting of Hastelloy, Inconel, Monel, andIncoloy.